The modern “mini-gun,” or M-134, can trace its origins to the original Gatling gun of the mid-nineteenth century. It is a machine gun which fires projectiles in an automatic fashion. In the process of firing these projectiles, the gun utilizes a plurality of barrels (usually six) which consecutively rotate in a circular circuit into a single position which allows for the firing of a projectile. Each barrel, then, is only used to fire one-sixth of the projectiles, spending the remaining time cooling in an air current caused by the rotation of the barrels. Over time, many improvements have been made to the original Gatling gun, resulting in the modern M-134. However, each variant of the M-134 has always featured the rotatable barrels which are the signature characteristic of this family of firearms.
Most modern firearms utilize cartridge ammunition. As cartridge is a fairly simple structure, with a projectile, or bullet, nested over an explosive charge of propellant. The charge and projectile are held together by a casing, or head. This casing presents a rearward primer which, when crushed, ignites and this ignition travels to the charge, igniting it explosively and thereby providing the impetus for launching the projectile. In most modern firearms, particularly with rifles, the primer is impacted by a firing pin. This firing pin is a spring-loaded hammer residing within a firearm bolt and, when released, impacts the primer of properly seated ammunition. The firearm bolt is also used to seat the next successive round of ammunition and, frequently, aids in the ejection of spent cartridges. Usually in an M-134 or Gatling variant each barrel will have its own bolt. The bolt usually has a body and a head which is movable with respect to the body.
The most commonly used M-134 bolt design in recent times is described in U.S. Pat. No. 3,611,866, issued in 1971 and assigned to the General Electric Company (the “GE Bolt”). A recent improvement is described in U.S. Pat. No. 6,742,434 to Dillon, (the “Dillon Bolt,” FIGS. 4 and 5). The standard operation of an M-134 with the GE Bolt is described at length in the '866 patent, which is herein incorporated by reference. The operation is virtually identical with the Dillon Bolt. To summarize, and using the Dillon Bolt as an illustration, the release mechanism is built into the firearm bolt 1 itself. The bolt follows a track on the inside casing of the receiver (FIG. 3), traveling a helical path such that the forwardmost position is the firing position. The bolt acquires an ammunition cartridge in its travel and, as it moves forward, chambers the cartridge. At this point, the bolt head 7 is against a barrel but the helical track continues forward. Following the continuing track forces the bolt carrier 2 and head 7 to compress against each other. A helical cam arm 5 cantileverally extending from the bolt head 7 interfaces with a helical cam slot 4 in the bolt carrier 2, causing the head 7 to twist in relation to the bolt carrier 2, while simultaneously the compression cocks the firing pin 3. When fully twisted, about ⅙ turn, the firing pin 3 releases and impinges the cartridge primer. The firing pin is spring-biased forward with a compression spring and a blocking pin located aft of the spring. It is also linked to the head of the bolt by a separate release pin interfacing with an L-shaped slot with transverse and longitudinal legs. In its default position, the release pin resides in the transverse leg of the slot. Thus, as the bolt head and carrier collapse against each other, the firing pin is biased against the spring as it is forced against the spring by its interaction with the transverse slot. When the bolt head and carrier reach their point of maximum rotational difference, the release pin is translated to the corner of the L-shaped slot. This translation frees the release pin, and thus the firing pin, for motion along the longitudinal leg. This releases the stored spring tension, allowing the firing pin to impinge a cartridge primer with enough force to cause an ignition of the propellant contained within the cartridge. As the firearm bolt cycles away from the forward-most position, the bolt head and carrier re-align, causing the engagement pin to relocate in the transverse leg of the L-slot, resetting for the next firing cycle.
One disadvantage of the GE Bolt involved the helical cam arm of the bolt head. As rotation was caused solely by the interaction of this single helical cam arm and a corresponding cam slot on the body, asymmetrical loads were placed on a singular and thin area of the bolt head. This caused a higher than desired rate of failure as these cam arms would occasionally break, rendering the bolt inoperative. This issue was addressed with the Dillon Bolt by adding a second helical cam arm 8 and cam slot 9 to the bolt structure to reduce the loads on a single cam arm 5; and, furthermore, the bolt could still function should one cam arm fail. However, while the Dillon Bolt is a marked improvement over the prior GE Bolt, it still places undue stress on two thin cantilevered appendages which, over time and with repeated loads, will eventually fail. What is needed is a firearm bolt which reduces or eliminates the loads placed on weaker areas of the structure while also being compatible with current M-134 designs.
The present invention represents a departure from the prior art in that the firearm bolt of the present invention allows for twisting of the bolt head in relation to the bolt body without utilizing a helical cam arm and slot system.